In the video processor art relating to cathode ray tube (CRT) display devices, the maintenance of good definition during constant scene changes with varying black-white contrasts have consistently plagued the users. Constant manual adjustments have been necessary for maintaining good contrast between the black and white levels for any specific viewing condition due to the variance in an individual viewer's eye as well as varying ambient viewing conditions of a changing scene.
The standard monochrome video processor has two controls, brightness and contrast. These controls must be used together when adjusting the displayed image. Brightness is controlled by adjusting the DC bias of the Gl to cathode voltage. The contrast is controlled by changes in the AC gain of the displayed video signal. Variations in the contrast affect both the broad area highlights as well as the broad dark areas. Also, fluctuations in the input signal will not be compensated in the displayed picture without adjustment of both brightness and contrast controls. The optimum picture should always contain a true black, not a gray shade as the minimum displayed brightness level.